Multiband tunable small antennas for modern mobile communication terminals

Abstract

Due to the rapid progress in the wireless communication technology and the ever increasing demand for multisystem applications, there is a growing trend toward the design of a multisystem handset. Recently, there are two major trends of mobile terminals. First one is multi-functions, second one is small and slim size handsets. Also mobile antenna has been an internal type. Furthermore, the antenna must have small, high efficiency, multiband, broadband, and low cost characteristics. For them, many antenna engineers have been researching about multi-wideband and small sized antenna. Especially, PIFA structure was very popular for antenna engineers due to the compactness, low profile, ease of manufacture and good electrical performance. Since PIFA has narrow operation frequency range, so many kinds of technique have been studied to make wide band and multi-band PIFA such as slot, parasitic patch, matching stub or capacitive load. Not only these technique but also tunable antenna technology can be another solution to overcome the disadvantages of PIFA. In this thesis, novel PIFA type varactor tunable antennas are proposed for mobile handset. There are several techniques for tunable antenna have proposed before such as, MEMS, PIN diode and varactor diode technique. Among them, varactor diode technique has good advantages of frequency tuning because varactor diode technique is based on the variation of capacitance so continues frequency shifting can be achieved. Firstly, a novel PIFA type varactor tunable antenna with U-shaped slot is proposed. This antenna occupies a compact volume of 40mm $times$ 15mm $times$ 8mm. A varactor diode is integrated between the slot and bias feeding strip line for tuning the operating frequency. This antenna covers from 1.64GHz to 2.05GHz refer to the dc bias voltage from 0V to 20V. The frequency tuning range covers DCS(1710~1880MHz), PCS(1750~1870MHz) and PCS(USA) (1850~1990MHz). This antenna was fabricated on FR4(Er=4.6) substra...